This proposal is focused on the de novo design of type 3 copper proteins. Peptides were designed so that they would assembled into an A2B2 tetramer with 2 symmetrical binding sites consisting of a mirror image of trigonal histidines. The intention for these histidines to binding Cu/II ions that could then bind to a side-on bridging peroxide ligand. After initial screening of binding and stability, we will produce a small library of peptides, with the aim of finding an optimal combination of ligating peptides. Successful sequences will be cloned and transformed into monomeric peptide units, linked by different turn regions. These evolved systems will be modified to allow for deficient diffusion of oxygen and other substrates. It is our aim, by designing these sites from scratch, to uncover some of the molecular details of the differences between the oxygen storing (i.e. hemocyanin) and catalytic systems (tyrosinase and catachol oxidase), seen naturally. We also aim to produce models that bind and convert phenols to catechols, capable of also performing oxidations. Furthermore, the design of these type of systems should allow us to systematically study the effect of ligand replacement (natural and unnatural) on the electronic structure of the copper centers, an area of intense research recently. The structure of the final models will e solved by high-resolution NMR.